AGRICULTURAL  EXPERIMENT  STATION 
UNIVERSITY    OF     CALIFORNIA  BENJ.  1DB  WHEELER,  PRESIDENT 

COLLEGE    OF    AGRICULTURE  thomas  forsyth  hunt,  dean  and  director 

H.    E.    VAN    NORMAN,    Vice-Director    and    Dean 

BERKELEY  university  farm  school 

CIRCULAR  No.  140. 

(OCTOBER,    1915) 

THE  PRACTICAL  APPLICATION  OF  IMPROVED  METHODS 

OF  FERMENTATION  IN  CALIFORNIA  WINERIES 

DURING  1913  AND  1914. 

By  Frederic  T.  Bioletti  and  W.  V.  Ceuess. 

The  fermentation  is  the  most  important  process  in  the  manufacture 
of  wine.  Most  inferior  wines  acquire  their  defects  during  this  process. 
The  finest  grapes  may  yield  inferior  wines  if  the  fermentation  is  not 
properly  conducted.  The  defects  increase  with  time  and  are  usually 
incurable.  On  the  other  hand,  any  sound,  ripe  grapes,  if  properly 
fermented,  will  yield  a  sound,  stable  wine  easily  handled  and  kept  and 
capable  of  developing  the  highest  possibilities  of  the  particular  raw 
material. 

By  the  application  of  modern  improved  methods,  it  is  possible  to 
avoid  nearly  all  the  defects  which  so  often  occur  in  wines  fermented  in 
the  old  hap-hazard  way.  The  most  important  of  these  methods  have 
been  thoroughly  tested  in  the  laboratory  and  the  winery.  They  are 
very  fully  discussed  in  Bulletins  167,  213,  and  230  of  this  Station. 

The  number  of  wineries  which  use  these  methods  increases  every 
year  and,  during  the  last  three  or  four  years  especially,  many  demands 
have  been  made  on  our  enological  laboratory  for  instruction  and  assist- 
ance in  introducing  needed  reforms  into  wineries  of  all  sizes.  During 
the  seasons  of  1913  and  1914,  a  special  effort  was  made  to  comply  with 
these  demands  and  improved  methods  were  introduced  into  a  consider- 
able number  of  wineries  in  various  sections  of  the  State.  The  principal 
reforms  were  the  use  of  sulfurous  acid  in  the  crushed  grapes  and 
the  application  of  selected  yeast.  The  results  justify  fully  the 
recommendations  of  the  laboratory  and  show  that  the  average  Cali- 
fornia wine-maker  can  avoid  all  trouble  from  spoiled  wine  if  he  adopts 
the  simple  and  inexpensive  means  described. 

In  order  to  judge  these  results,  the  wines  from  twenty  wineries  in 

1913    and   from   twenty-two    in    1914   were    carefully   examined   and 

analyzed.     Observations  were  made  on  the  methods  adopted  in  these 

various  wineries,  which  included  both  those  which  used  the  new  methods 

19119 


—  2  — 

and  similar  establishments,  usually  in  the  same  locality,  which  con- 
tinued the  old  methods.  A  comparison  of  the  wines  from  the  two 
classes  of  wineries  gives  very  striking  evidence  of  the  value  of  the  new 
methods. 

The  wineries  investigated  are  situated  in  the  counties  of  Sonoma, 
Napa,  Contra  Costa,  Alameda,  Santa  Clara,  San  Joaquin,  Sacramento, 
and  San  Diego,  principally  in  the  first.  The  wines  made  ranged  from 
very  good  to  bad,  but  no  spoiled  wines  were  made  in  the  cellars  where 
the  new  methods  were  used. 

The  methods  of  wine-making  varied  somewhat  in  the  different 
wineries,  differing  principally  in  the  care  and  the  promptness  with 
which  the  various  operations  were  carried  out.  In  a  few,  sulfurous 
acid  and  pure  yeast  have  been  in  use  for  several  years;  in  most,  these 
improvements  were  introduced  for  the  first  time  in  1913  or  1914. 
Below  are  given  (1)  the  methods  tested  and  the  mode  of  application; 
(2)  the  results  of  the  examination  of  the  wines,  and  (3)  a  discussion  of 
these  results. 

METHOD    OF    APPLYING    THE    SULFUROUS    ACID    AND    PURE    YEAST. 

Preparation  and  use  of  the  selected  yeast.  In  the  district  where  most 
of  the  work  was  done,  a  pure  culture  of  "Burgundy"  wine  yeast  was 


Fig.  I.     Materials    necessary    for    the    in- 
crease of  the  pure  yeast  to  two  gallons. 


grown  and  increased  to  50  gallons  at  the  winery  by  a  representative  of 
the  Viticulture  Division  in  the  following  way: 

1.  A  quart  bottle  containing  some  pure  yeast  in  solid  form  was 


6  — 


nearly  filled  with  sterilized  grape  juice  and  left  in  a  warm  place  (see 
Fig.  I  and  Fig.  IY  a,  b). 


Hn 


Fig.  II.  "Wash  boiler  sterilizer  used  to 
sterilize  the  juice  in  the  three-gallon  demi- 
john. 

2.  In  the  mean  while,  2  gallons  of  juice  in  a  three-gallon  demijohn 
was  sterilized  in  a  wash  boiler  (see  Fig.  II).  A  screen  was  placed 
under  the  demijohn  to  protect  it,  the  demijohn  plugged  with  cotton,  the 


Fig.  III.     Boiler  used  to  sterilize  thirty  gallons  of  juice 
at   165   degrees  F.   for  growth   of  yeast. 

boiler  half  filled  with  cold  water,  the  lid  of  the  boiler  placed  on  tight, 
and  finally,  the  water  was  heated  to  boiling  and  kept  boiling  for  about 
half  an  hour  to  sterilize  the  juice. 


—  4  — 

3.  Twenty-four  hours  later,  the  first  quart  of  yeast  was  fermenting 
and  was  poured  into  the  2  gallons  of  sterilized  juice  in  the  demijohn 
(see  Fig.  I  and  Fig.  IV  c). 

4.  The  demijohn  was  then  left  in  a  warm  place  to  incubate. 

5.  Next,  30  gallons  of  juice  was  heated  to  about  165°  F.  in  a  clean 
iron  boiler  (see  Fig.  III).  This  juice  was  then  transferred  to  a  clean, 
open  50-gallon  barrel  covered  with  a  piece  of  clean  canvas  and  allowed 
to  settle  and  cool  to  90°  F.  (see  Fig.  IV  d). 

6.  The  two  gallons  of  juice,  which  by  this  time  was  fermenting 
vigorously,  was  then  poured  into  the  30  gallons  of  clear  sterile  juice 
previously  run  into  an  open  50-gallon  barrel  (see  Fig.  IV  /). 

7.  The  inoculated  juice  in  the  barrel  was  aerated  several  times  a  day 
by  pouring  it  through  the  air  back  into  the  barrel  with  a  large  dipper 
previously  sterilized  in  hot  water.  "When  the  temperature  fell  below 
90°  F.  it  was  brought  up  again  by  the  addition  of  hot  water,  added 
very  slowly  and  with  vigorous  stirring  to  avoid  killing  the  yeast  by 
scalding. 


FIG.  IV.   A  simple  yeast  propagating  apparatus. 
a.   Pure  yeast,  solid  culture,  from  University, 
b    and    c.   Sterilized   juice. 

d.  Settling  barrel   for  fresh  juice. 

e.  Dipper  to  aerate  yeast  in   "f." 

f.  Yeast  barrel. 

8.  Other  wineries  of  the  district,  desiring  to  use  the  yeast,  sterilized 
40-gallon  lots  of  juice  in  50-gallon  barrels  by  the  use  of  steam  intro- 
duced directly  into  the  juice  by  means  of  a  hose.     When  this  juice 


cooled  to  90°  F.,  a  gallon  or  two  of  the  yeast  produced  at  the  first 
winery  was  supplied  to  each  of  the  others  and  used  to  inoculate  the  40 
gallons  of  sterile  juice.  The  settling  and  racking  described  under  6  are 
not  essential. 

9.  When  the  yeast  in  the  barrel  was  fermenting  vigorously  and  was 
seen  to  form  the  characteristic  thick  scum  and  heavy  granular  sediment 
of  the  "Burgundy"  yeast,  the  first  vat  of  grapes  was  crushed.  As  the 
grapes  were  crushed,  potassium  metabisulfite  solution  containing 
10  ounces  of  metabisulfite  per  gallon  was  added  at  the  rate  of  1  gallon 
per  ton  and  thoroughly  mixed  in.  About  three  hours  later,  the  whole 
30  to  50  gallons  of  yeast  was  added  and  the  vat  thoroughly  punched 
to  mix  and  aerate  the  yeast  (see  Fig.  VII). 


Fig.  V.  A  five-gallon  demijohn  marked  in  gallons  and 
fitted  with  adjustable  syphon.     For  details  see  Fig.  VI. 

10.  When  this  vat  was  in  vigorous  fermentation,  it  was  used  to  start 
the  next  vat  of  grapes  treated  with  metabisulfite  in  the  same  manner  that 
the  first  had  been.  This  vat  in  turn  was  used  to  start  the  third  vat,  and 
so  on,  progressively  through  the  vintage. 

In  all  the  wineries,  except  the  first,  the  yeast  was  grown  by  the  wine 
makers  themselves,  without  our  supervision. 

This  method  has  been  given  in  detail  because  it  is  simpler  and  has 
given  better  results  in  practice  than  the  method  recommended  in  our 
Bulletin  230.  It  reduces  the  chance  of  the  wine  maker's  committing 
any  serious  mistake  in  the  manipulation  of  the  yeast. 

Application  of  the  sulfurous  acid.  In  using  any  form  of  sulfurous 
acid  it  is  necessary  to  measure  the  amount  accurately,  to  apply  it  as 
soon  as  possible  after  the  crushing  of  the  grapes  and  to  distribute  it 
quickly  and  evenly  throughout  the  whole  mass.  With  potassium  metabi- 
sulfite this  is  most  easily  accomplished  by  dissolving  the  sulfurous  salt 
in  water  in  a  definite  proportion.     A  convenient  solution  is  one  which 


6  — 


contains  in  each  gallon  the  amount  of  the  salt  needed  for  one  ton  of 
grapes.  The  solution  used  in  the  fermentations  described  here  contained 
10  ounces  in  each  gallon. 

Figure  VI  shows  a  convenient  and  simple  device  for  measuring  and 
distributing  such  a  solution.    "When  the  reservoir  is  filled,  the  amount  to 


To  Crushing  Sump 


Fig.  VI.     Device    for    measuring    and    regulating 
metabisulfite    solutions. 
A.  Reservoir    (5-gallon    demijohn)    marked   with 
lines  indicating  half  gallons. 

a.  Inlet  for  air  and  for  filling. 

b.  Perforated  rubber  stopper. 

c.  Exit  tube  to  fix  the  amount  of  solution  used. 

d.  Pinch   cock   to   start   or   stop   the   flow   of   the 
solution. 

e.  Screw  cock  to  regulate  the  rate  of  flow. 

f .  Rubber   tube   syphon   to   draw  off  the   solution 
and  to  deliver  it  to  the  crushed  grapes. 

be  applied  is  determined  by  the  level  of  the  bottom  extremity  of  the 
outlet  tube;  the  3|  gallons  in  the  case  illustrated  is  enough  for  3J  tons 
of  crushed  grapes.  The  rate  of  flow  is  regulated  by  the  screw  cock 
attached  to  the  rubber  syphon  tube  /.    This  cock  should  be  so  adjusted 


—  7  — 

that  a  gallon  of  solution  flows  out  during  the  time  needed  to  crush  one 
ton  of  grapes.  The  flow  is  started  by  removing  the  spring  cock  d  and 
stopped  by  replacing  it.  The  device  may  be  placed  on  a  board  over  the 
vat  which  is  being  filled  or  over  the  crushing  sump. 


Fig.  VII.     The    yeast    is   mixed   with    the    crushed    grapes   by 
thorough  punching  or  by   other  suitable   means. 

The  wineries  used  as  checks  employed  the  "let  alone"  or  "sponta- 
neous" method  of  fermentation,  where  the  grapes  are  simply  crushed 
and  allowed  to  ferment  spontaneously.  No  sulfurous  acid  was  used 
in  these  wineries. 


Fig.  VIII.  A  typical  "frothy"  spontaneous  fermentation. 
Pure  Burgundy  yeast  in  contrast  to  this  gives  a  very  quiet 
but  rapid   fermentation. 

No  cooling  apparatus  was  used,  except  in  one  Contra  Costa  County 
winery.  Consequently,  many  of  the  fermentations,  both  with  and  with- 
out pure  yeast  or  sulfurous   acid  became  very  hot;  in  many  cases 


under  observation,  temperatures  of  104  and  105°  F.  being  reached. 
The  results  of  the  high  temperatures  are  shown  in  the  naturally 
fermented  wines  by  the  presence  of  very  large  amounts  of  volatile  or 
" vinegar"  acid.  The  low  volatile  acid  in  all  the  wines  made  by  the 
new  method  is  proof  of  its  efficiency  in  producing  sound  fermentations 
even  at  the  "sticking"  temperatures  of  104  and  105°  F. 

ANALYSIS   AND    EXAMINATION    OF   WINES    AFTER    FERMENTATION. 

At  about  the  time  of  the  first  racking,  samples  of  each  tank  were  sent 
from  the  various  wineries  to  the  enology  laboratory.  Because  the 
amounts  of  volatile  acid,  alcohol,  and  sugar  a  wine  contains  and  the 
character  and  number  of  bacteria  that  it  carries  are  the  most  important 
criteria  by  which  the  soundness  of  a  wine  may  be  judged,  most  attention 
was  given  to  these  data.  Analyses  of  other  constituents  of  the  wines 
were  made,  but,  since  they  have  little  bearing  on  the  points  involved  in 
this  publication,  they  are  not  included  in  the  tables.  To  save  space  and 
to  make  the  results  clearer,  the  average  composition  of  the  wines  of  each 
cellar  has  been  given  instead  of  an  extended  list  of  all  the  individual 
wines.  The  methods  of  analysis  are  those  followed  by  California  wine 
chemists.  The  bacterial  contents  of  the  wines  were  determined  by 
microscopical  examination.  A  wine  at  the  first  racking  containing  only 
yeast  cells  is  normal;  one  containing  large  numbers  of  bacteria  is 
unsound.  A  sound  dry  wine  should  have  less  than  .1%  volatile  acid;  if 
the  percentage  is  above  .140%  the  wine  is  considered  spoiled.  It  should 
not  contain  more  than  .3%  sugar  unless  very  sound  otherwise.  In 
general,  the  amount  of  volatile  acid  is  by  far  the  most  important  test 
of  a  wine's  soundness  and  in  studying  the  following  tables,  most 
attention  should  be  paid  to  this  constituent. 


—  9 


Table   I. 


Composition   of  1913   Wines  Classified   According  to   District  and    Method  of 
Fermentation. 


Locality 


n| 

2 

> 

> 

p  c 

^2 

»B 

S4 

ELo- 

im  (° 

yf  CD 

BS 

1* 

P 

JD0 

•a  o 

*S 

1     tB 

Us 

•  B 

!  '2. 

§J 

SBL 

i  m 

«5 

ra 

Microscopical 
examination 


.1.     Fermented  Usual  Way — No  Sulfurous  Acid  nor  Pure  Yeast. 


*1 

2 

8 

9 

10 

11 

12 

15 

20 

4 

9 
6 
6 
5 

7 
7 
7 
44 
5 
5 

.122 
.205 
.147 
.072 
.088 
.100 
.082 
.122 
.129 
.091 

.75 
.86 
.81 
.62 
.58 
.61 
.75 
.63 
.54 
.56 

12.27 
12.26 
13.16 
12.75 
11.94 
12.21 
11.61 
10.70 
12.15 
11.43 

.39 
.61 
.36 
.46 
.26 
.19 
.36 
.71 
.11 
.17 

Sonoma  County  _        

Many  long  rod  bacteria 

Sonoma  County 

Many  long  rod  bacteria 

Many  long  rod  bacteria 
Many  long  rod  bacteria 

Sonoma  County 

Sonoma  County 

Many  long  rod  bacteria 

Sonoma  County 

Sacramento  County 

San  Joaquin  County 

Santa  Clara  County 

Many  long  rod  bacteria 
Many  long  rod  bacteria 
Many  long  rod  bacteria 
Many  long  rod  bacteria 

Averages 

101 

.118 

.66 

11.54 

.49 

Total  number  samples 

B.     Fermented 

With  Sulfurous  Acid.     No  Pure 

Yeast. 

Sonoma  Ccunty _._ 

Sonoma  County 

8 
4 

5        .043 
1         .053 

.45 
.55 

13.65 
11.50 

.41 
.44 

Yeast  cells  only 
Yeast  cells  only 

.048 

6| 

.50 

12.57 

.42 

Total  number  samples 

C.     Fermented  With  Sulfurous  Acid  and  Pure  Yeast. 

Sonoma  County  

3 

5 
6 
7 
14 
16 
17 
18 
19 

4 

11 
6 
2 
3 
7 
13 
8 
13 

.067 
.055 
.050 
.071 
.046 
.049 
.056 
.083 
.091 

.55 
.66 

.58 
.48 
.77 
.56 
.49 
.66 
.51 

13.15 
11.45 
13.90 
12.30 
12.20 
11.68 
12.00 
11.73 
11.90 

r9A 

Yeast  cells  only 
Yeast  cells  only 
Yeast  cells  only 
Yeast  cells  only 
Yeast  cells  only 
Yeast  cells  only 
Yeast  cells  only 
Yeast  cells  only 
Yeast  cells  only 

Sonoma  County 

19 

25 
72 
66 
06 
06 
32 
IS 

Sonoma  County  _- 

Sonoma  County  

San  Diego  County. 

Napa  County 

Contra  Costa  County 

Contra  Costa  County 

Averages   

67 

.066 

.57 

12.08 

,21 

Total  number  samples 

'The    winery   numbers   for   1913    do   not   correspond   with  those   for   1914. 


10 


Table  II. 


Composition  of  1914  Wines  Classified  According  to  District  and  Method  of 
Fermentation. 


Locality 


2 

Off 

?•  s 

IS 

SB 

a.  8, 

s 

i 

« 

CO 

P  a 


► 

► 

o  3 

II 

is 

■O  » 

•to 

«  S* 

-s  e 

S| 

OP 

» M 

f5 

; 

■ 

Microscopical 
examination 


A.     Fermented  Usual  Way — No 

Sulfur  ous  Acid  nor 

Pure  Yeast. 

Sonoma  County 

1 
2 
3 
4 
5 

9          .060 

4  .059 
1          .071 

5  .060 
3          .159 

.59       12.91 
.68       11.11 
.57       11.80 
.64       12.18 
.68       13.06 
.68       13.10 
.70  !     12.06 
.60  j    11.84 
.63       11.31 
.78        12.66 

.20     Yeast  cells  only 

Sonoma  County 

Sonoma  County 

Sonoma  County 

.36     Many  long  rod  bacteria 
.21     Many  long  rod  bacteria 
.12     A  few  bacteria 
.10     A  few  bacteria 
.10     Yeast  cells  only 

Sonoma  County  

Sonoma  County 

Sonoma  County  _ .__ 

Sonoma  County 

Sonoma  County 

6 

7 

8 

9 

10 

1 

6 
7 
6 
5 
9 
1 
3 
1 
3 

4 

.100 
.033 
.057 
.045 
.151 
.093 
.181 
.049 
.075 
.079 

.324 

Sonoma  County 

Sonoma  County 

Sonoma  County 

Sonoma  County 

Contra  Costa  County 

Oakland  (from  San  Joa- 
quin County  grapes) 

11 
12 
13 
14 
19 

20 

.78 
.67 
.67 
.79 

1.01 

11.17 
11.40 
12.20 
13.20 
12.80 

.08 

.51 

.40 

A  few  long  rod  bacteria 
Many  long  rod  bacteria 
.  Yeast  cells  only 
Many  long  rod  bacteria 
Many  long  rod  bacteria 

Many  long  rod  bacteria 

68 

.088 

.61 

12.07 

.20 

Total  number  samples 

B.     Fermented  With  Use  of  Sulfurous  Acid  and  Pure  Yeast. 

g 

15 
16 
17 
18 
12 
21 
22 

16          .057 
3   :       .040 
7  !       .048 
6         .063 
3  !       .045 
2          .051 

14          .047 
5          .053 

.55       11.89 
.82  !     11.49 
.68       12.84 
.64       12.34 
.66       11.16 
.50       11.07 
.64       12.05 
.63       12.54 

.36 
.28 
.25 
.22 
.04 
.09 
.18 
.14 

Yeast  cells  only 

Sonoma  County 

Yeast  cells  only 

Yeast  cells  only 

Veast  cells  only 

Yeast  cells  only 

Napa  County 

Yeast  cells  only 

San  Diego  County 

Yeast  cells  only 

.052 
56 

.62       12.07 

.24 

Total  number  samples 

—  11 


DISCUSSION    OF  TABLES. 


Table  I.  1913  Wines.  The  most  striking  features  of  the  analyses  of 
the  1913  wines  are  the  very  high  volatile  acid,  sugar,  and  bacterial 
contents  of  the  wines  made  in  the  usual  way.  This  indicates  a  large 
number  of  "stuck  wines";  i.  e.,  wines  in  which  yeast  fermentation  has 
been  stopped  by  high  temperature  or  other  causes  and  in  which  acid- 
producing  bacterial  fermentations  usually  set  in.  Thirty  of  the  101 
naturally  fermented  wines  were  above  the  legal  maximum  of  .140% 
in  volatile  acid.  Such  wines  are  ' '  spoiled ' '  and  fit  for  distilling  material 
only.  Forty-nine  of  these  wines,  or  approximately  50%,  were  above 
.1%  of  volatile  acid,  the  maximum  for  a  sound  new  wine.  In  other 
words,  approximately  one-third  of  the  spontaneously  fermented  wines 
were  spoiled  and  one-half  of  them  would  spoil  if  not  given  special 
treatment  to  check  bacterial  action. 

On  the  other  hand,  none  of  the  wines  made  by  the  improved  method 
were  above  .140%  volatile  acid  and  only  three  out  of  a  total  of  67  wines 
were  above  .1%.  The  wines  in  both  cases  were  made  from  similar 
grapes  and  most  of  the  wines  under  observation  reached  very 
high  temperatures  during  fermentation  owing  to  the  very  hot  weather 
during  the  fermenting  season.  Temperatures  above  100°  F.  were  the 
rule  and  many  vats  both  with  and  without  sulfurous  acid  and  pure  yeast 
reached  a  temperature  of  105°  F.  But  the  behavior  of  the  wines  in 
which  the  sulfurous  acid  and  pure  yeast  were  used  was  very  different 
from  that  of  those  fermented  in  the  ordinary  way.  In  the  former  wines, 
the  yeast  recovered  when  the  wines  cooled  and  fermentation  of  the 
remaining  sugar  was  completed  without  any  appreciable  injury  to  the 
quality  of  the  wines.  But  the  yeast  in  the  spontaneously  fermented 
wines  did  not  recover  and  after  the  wines  "stuck"  at  105°  F.,  vinegar 
and  "  mousey- wine "  bacteria  increased  rapidly  and  turned  the  wines 
more  or  less  vinegar  sour.  This  demonstrates  that  it  is  possible  to 
obtain  sound  fermentations  even  at  high  temperatures  when  sulfurous 
acid  and  selected  yeast  are  used. 

Table  II.  1914  Wines.  The  fermenting  season  of  1914  was  excep- 
tionally cool.  Hot  fermentations  were  therefore  less  common  than  in 
1913  and  spoiled  wines  were  rare.  But  even  under  these  exceptionally 
favorable  conditions,  ten  out  of  a  total  of  68  spontaneously  fermented 
wines  were  spoiled,  i.  e.,  contained  more  than  .140%  volatile  acid  and 
15  were  above  the  limit  of  .1%.  On  the  other  hand,  all  of  the  wines 
fermented  with  sulfurous  acid  and  pure  yeast  were  below  .140%  and 
only  two  out  of  a  total  of  56  were  above  .1%.  The  average  volatile  acid 
(.0878%)  of  the  wines  made  in  the  usual  way  was  68%  higher  than  the 
average  (.052%)  of  the  wines  made  by  the  improved  methods. 


—  12  — 


Table    III.     Summary   of   Volatile    Acid    Content   of   1913   and    1914   Wines. 


Year  and  method  of  fermentation 

Maximum 
volatile 

acid, 
per  cent 

Minimum 
volatile 

acid, 
per  cent 

Average 
volatile 

acid, 
per  cent 

Per  cent  of  |  Per  cent  of 
wines  above  |  wines  above 

.14  per  cent  .1  per  cent 
volatile  acid  volatile  acid 

Number  of 
samples 
analyzed 

1913  ordinary  fermentation 

1913  SO-  only 

.290 
.053 
.118 
.537 
.085 

.044 
.088 
.026 
.023 
.023 

.1180 
.0480 
.0660 
.0878 
.0520 

29.7 

0 

0 
14.7 

0 

48.5 

0 

4.4 
22.0 

3.6 

101 
6 

1913  SO2  and  pure  yeast 

67 

1914  ordinary  fermentation 

1914  SO2  and  pure  yeast . 

68 
56 

The  summary  shown  in  Table  III  brings  out  some  interesting  facts. 
It  is  to  be  noted  that  the  maximum  volatile  acid  of  .118%  found  during 
1913  in  a  wine  fermented  by  the  new  methods  was  exactly  the  same 
as  the  average  for  all  the  wines  made  in  the  old  way.  In  1914  it 
was  slightly  less.  The  maximum  for  1913  was  slightly  above  the 
normal  limit  for  a  new  wine,  that  of  1914  slightly  below.  This  indicates 
that,  where  the  conditions  are  unfavorable,  as  in  1913,  and  the  cellar 
work  inferior,  even  the  use  of  sulfurous  acid  may  be  insufficient  to 
save  the  wine.  It  may,  however,  simply  mean  that  in  the  fermentation 
of  this  particular  wine  the  method  was  imperfectly  applied,  which  is 
very  probable  where  so  many  cellars  and  so  many  wines  are  involved. 

The  excessively  high  maximum  of  .535%  in  1914  for  a  wine  fermented 
in  the  ordinary  way  shows  that  even  when  the  weather  conditions  are 
favorable,  careless  methods  may  result  in  absolutely  spoiled  wines. 

On  the  other  hand,  the  extremely  low  minimum  of  .023%  for  the 
same  year  shows  that  under  favorable  conditions  a  good  wine  maker 
can  make  good  wines  by  the  old  methods.  In  the  winery  where  this 
wine  was  produced,  however,  the  average  volatile  acid  of  the  wines  of 
1913,  when  the  conditions  were  unfavorable,  was  .088%  while  that  of 
wines  made  in  wineries  using  the  new  methods  and  representing  all 
degrees  of  skill  and  lack  of  skill  was  only  .066%,  indicating  that  even 
great  care  is  sometimes  insufficient  with  the  old  methods. 

Table    IV.     Relative    Stability   of   Spontaneously    Fermented    Wines   and    Wines    Fer- 
mented  With   Pure  Yeast  and   Sulfurous  Acid  as   Indicated   by 
Changes   in   Volatile   Acid. 


Wine 

Volatile  acid 

before 

incubation  at 

95°  F.,  per  cent 

Volatile  acid 

after  six  days' 

incubation  at 

95°  F.,  per  cent 

Increase  in 

volatile  acid, 

per  cent 

Blend  of  all  Sonoma  County  naturally  fermented 
wines,  1913 

.180 
.075 

.240 

.080 

.060 

Blend  of  all  Sonoma  County  wines  fermented  with 

.005 

Relative  Stability  of  Wines  Made  by  the  Two  Methods.  The  stability 
or  keeping  quality  of  a  wine  may  be  judged  by  its  resistance  to  warm 
temperatures.     A  blend  of  all  the  samples  from  Sonoma  County  made 


—  13  — 

by  the  usual  method  in  1913  and  a  blend  of  all  the  wine  from  the  same 
district  made  by  the  new  method  were  incubated  in  well-filled  and 
corked  demijohns  at  95°  F.  The  volatile  acid  content  before  and  after 
incubation  was  used  as  a  measure  of  the  amount  of  deterioration  taking 
place.  Table  IV  shows  the  results.  The  volatile  acid  of  the  wine  made 
by  the  usual  method  increased  by  one-third  in  six  days  while  that  of  the 
wine  made  with  the  aid  of  sulfurous  acid  and  pure  yeast  remained 
practically  stationary.  In  other  words,  the  former  deteriorated  very 
rapidly  at  95°  F.  for  the  short  period  during  which  the  wines  were 
under  observation,  while  the  latter  remained  stable.  This  would  indi- 
cate a  similar  ratio  of  stability  during  aging  of  the  wines  at  the  ordinary 
cellar  temperatures. 

Table    V.     Sulfurous   Acid    (S02)    Contents   of   Wines    Fermented    With    Metabisulfite 

and  Pure  Yeast. 


Number  of  samples  analyzed ..        26  wines 

Average  amount  of  SO2  added  to  grapes— mg.  per  liter 175  mg. 

Average  amount  of  SO2  found  in  wines  at  first  racking _.       64  mg. 

Maximum  amount  of  SO2  found  in  wines  at  first  racking 1!)2  mg. 

Average  loss  of  SO2  to  time  of  first  racking  (63.5%) 111  mg. 


Amount  of  Sulfurous  Acid  Remaining  in  Wines  at  First  Backing. 
The  pure  food  law  allows  a  maximum  of  300  milligrams  of  sulfurous 
acid  per  liter  or  .03%.  An  examination  of  Table  V  will  remove  any 
doubt  as  to  whether  wines  treated  with  the  usual  amounts  of  metabisul- 
fite during  fermentation  retain  an  excessive  amount  of  sulfurous  acid. 
The  maximum  found  was  192*  milligrams  of  sulfurous  acid  per  liter, 
while  the  average  was  only  64  milligrams  per  liter  or  .0064%.  That 
is,  the  average  was  only  about  21%  of  the  legal  limit  and  the  maximum 
only  64%.  The  crushed  grapes  were  treated  with  approximately  10 
ounces  of  potassium  metabisulfite  per  ton,  which  corresponds  to  about 
170  to  175  milligrams  sulfurous  acid  per  liter  or  .0170  to  .0175%. 
Thus,  roughly  speaking,  two-thirds  of  the  sulfurous  acid  disappeared 
between  the  time  of  crushing  and  first  racking. 

SUMMARY  AND  CONCLUSIONS. 

1.  Pure  yeast  and  sulfurous  acid  can  be  applied  successfully,  on  a 
practical  scale,  by  the  average  wine  maker  by  the  method  outlined  in 
this  publication. 

2.  The  application  of  this  improved  method  resulted  in  more  perfect 
fermentations  and  in  sounder  wines,  showing  marked  improvement 
over  wines  fermented  in  the  usual  way  in  the  same  locality.  The 
improved  method  gave  sound  wines  even  where  the  excessively  high 
temperature  of  105°  F.  was  reached  during  fermentation,  while  the 

.     *This  wine  undoubtedly  received  more  than  the  amount  of  sulfite  recommended. 


—  14  — 

wines  made  in  the  usual  way  in  such  eases  "stuck"  and  became  vinegar 
sour. 

3.  Sulfurous  acid  alone  seemed  to  give  just  as  sound  wines  as  where 
pure  yeast  was  used  in  addition  to  the  sulfurous  acid. 

4.  Wine  made  by  the  improved  method  kept  a  great  deal  better  at 
warm  temperatures  than  the  spontaneously  fermented  wine. 

5.  The  amount  of  sulfurous  acid  left  in  the  wine  is  well  below  the 
pure  food  limit. 

6.  The  observations  made  in  1913  and  1914  confirm  fully  the  con- 
clusions given  in  our  Bulletin  230. 


